Final answer:
The exact number of newsroom supervisors who were women in 2015 is not provided, but women's representation in newsrooms has been increasing over time.
Step-by-step explanation:
In 2015, the exact number of newsroom supervisors who were women is not provided in the given information. However, the information mentioned Barbara Walters as the first woman coanchor on a network news show in 1976. This suggests that the presence of women in newsrooms has been increasing over time. Additionally, the Center for American Women in Politics researches the treatment of women in the media and shares data on women's representation.